Method for charging secondary battery and charger therefor

Abstract

The present invention provides a method for charging a secondary battery and a charger by which it can be prevented that a secondary battery is charged at very high or low temperature, and that the secondary battery is charged for a long time. Therefore, the secondary battery is prevented from being damaged, so that the lifetime can be prolonged. In this method, a generally constant current is supplied from a charging means to the secondary battery. The constant-current charging is stopped when voltage of the secondary battery has reached a peak value after passage of a predetermined time period from start of the supplying of the first current; temperature of the secondary battery has been out of a predetermined range; or a predetermined time period has passed since start of the supplying of the first current.

We claim: 
     
       1. A method for charging a secondary battery comprising the steps of supplying a first current, which is generally constant, from a charging means to the secondary battery, and checking each of the following conditions and stopping the supply of the first current when any one of the them is fulilled: (A) the voltage of the secondary batter has reached a peak level after passage of a predetermined time period from start of the supplying of the first current; (B) the temperature of the secondary battery is out of a predetermined range; and (C) a predetermined time period has passed since start of the supplying of the first current, checking as to whether the temperature of the secondary battery is in a predetermined range after connecting of the secondary battery and charging means; and only proceeding to the step of supplying the first current if the temperature of the secondary battery is in the predetermined range, supplying a second current which is constant and lower tan the first current, only if the supply of the first current has stopped for the reason of the condition (A) or (B), waiting until the temperature of the secondary battery falls to be below a predetermined level; and then indicating that the charging has ended. 
     
     
       2. A method for charging a secondary battery comprising the steps of supplying a first current, which is generally constant, from a charging means to the secondary battery, and checking each of the following conditions and stopping the supply of the first current when any one of the them is fulfilled: (A) the voltage of the secondary battery has reached a peak level after passage of a predetermined time period from start of the supplying of the first current; (B) the temperature of the secondary battery is out of a predetermined range; and (C) a predetermined time period has passed since start of the supplying of the first current, checking as to whether the temperature of the secondary battery is in a predetermined range after connecting of the secondary battery and charging means; and only proceeding to the step of supplying the first current if the temperature of the secondary battery is in the predetermined range, supplying a second current which is constant and lower than the first current, only if the supply of the first current has stopped for the reason of the condition (A) or (B), checking as to whether the temperature of the secondary battery is in a predetermined range or not before and at the step of supplying the second current; and supplying the second current insofar as the temperature of the secondary battery is in the predetermined range. 
     
     
       3. A method for charging a secondary battery comprising the steps of supplying a first current, which is generally constant, from a charging means to the secondary battery, and checking each of the following conditions and stopping the supply of the first current when any one of the them is fulfilled: (A) the voltage of the secondary battery has reached a peak level after passage of a predetermined time period from start of the supplying of the first current; (B) the temperature of the secondary battery is out of a predetermined range; and (C) a predetermined time period has passed since start of the supplying of the first current, checking as to whether the temperature of the secondary battery is in a predetermined range after connecting of the secondary battery and charging means; and only proceeding to the step of supplying the first current if the temperature of the secondary battery is in the predetermined range, waiting until the temperature of the secondary battery falls to be below a predetermined level; and then indicating that the charging has ended. 
     
     
       4. A method for charging a secondary battery as defined in claim 1 further comprising steps of checking as to whether the voltage of the secondary battery is above a predetermined level after at least one of the steps of supplying the first current and supplying the second current; and supplying the first current again if the voltage of the secondary battery is not above the predetermined level. 
     
     
       5. A method for charging a secondary battery as defined claim 1, further comprising a step of waiting a certain period after the temperature of the secondary battery falls to be in the predetermined range if the temperature of the secondary battery has been above the predetermined range in the step of checking the temperature before proceeding to the step of the supplying the first current. 
     
     
       6. A battery charger capable of supplying a generally constant current to a second battery, comprising: current generating means for generating a constant current; counting means for counting time from start of charging of the secondary battery; voltage detecting means for detecting voltage of the secondary battery; temperature detecting means for detecting temperature of the secondary battery; and controlling means for controlling supply of the constant current from the current generating means to the secondary battery, said controlling mean stopping the supply of the current when any one of the following conditions is fulfilled: (A) the voltage detected by said voltage detecting means has reached a peak level after the counting means counts a predetermined time period from start of the supplying of the current; (B) the temperature detected by the detecting means is out of a predetermined range; and (C) the counting means has counted a predetermined time period, the current generating means generating a first current and a second current which is lower than the first current, the controlling means initially supplies the first current to the secondary battery and thereafter supplies the second current after stopping the supply of the first current for the reason of the condition (A) or (B), and means for deciding to finish of the supply of the second current, and indicating means for indicating end of the charging when the temperature detected by the temperature detecting means falls to a predetermined level. 
     
     
       7. A battery charger as defined in claim 6, wherein the controlling means checks if the temperature of the secondary battery is in a predetermined range before and during the supplying the second current, and permits the supply of the second current only when the temperature detected by the temperature detecting means is in the predetermined range. 
     
     
       8. A battery charger capable of supplying a generally constant current to a secondary battery, comprising: current generating means for generating a constant current; counting means for counting time from start of charging of the secondary battery; voltage detecting means for detecting voltage of the secondary battery; temperature detecting means for detecting temperature of the secondary battery; and controlling means for controlling supply of the constant current from the current generating means to the secondary battery, said controlling mean stopping the supply of the current when any one of the following conditions is fulfilled: (A) the voltage detected by said voltage detecting means has reached a peak level after the counting means counts a predetermined time period from start of the supplying of the current; (B) the temperature detected by the detecting means is out of a predetermined range; and (C) the counting means has counted a predetermined time period, sand means for detecting that the counting means has counted a predetermined time period, thereafter terminating the supply of the constant current to the secondary battery, and indicating means for indicating end of the charging when the temperature detected by the temperature detecting means falls to a predetermined level. 
     
     
       9. A battery charger as defined in claim 6, wherein the controlling means checks when the voltage detected by the voltage detecting means is above a predetermined level after supplying at least one of the first current or the second current, and supplies the first current again if the voltage detected by the voltage detecting means is not above the predetermined level. 
     
     
       10. A battery charger as defined in claim 6, further comprising second counting means for counting time from after the temperature o the secondary battery falls in the predetermined range if the temperature detected by the temperature detecting means has been above the predetermined range, the controlling means starts to supply the current to the secondary battery after that the second counting means has counted a predetermine time period.